user88: I just can't help to notice that there are quite a lot of questions that already have answers, and those answers are quite sensible but the user who asked those questions haven't accepted the answer yet. (You can reference to the Unanswered tab for those questions)
Reasons might be because the user is still waiting for a better answer to come and I understand that. But when the question has been hanging for a quite a long time, the user who asked the question might already forget to accept the answer and the user who answered the question will be left hanging. Of course it will cause the user to be discouraged, since all of us would like to gain more reputations and badges. 
I am referring especially to those new users who answered questions (and of course for all the users' benefit in general). For them not to be discourage and leave the site because they don't get any motivations (reputations or badges) when answering questions.
I suggest having the users check the questions they asked and validate whether there will still be a better answer to come (when the question has been not active for quite a time) and if they can consider accepting the answer available. This is my suggestion and it is okay for you guys to correct me if I'm wrong. 

user24: This MSO post is essentially asking about the same thing.
It is reasonable to suggest that the OP accept an answer if it's likely that they do not know about accepting answers. This is especially the case if they leave comments on an answer thanking the answerer. New users who have not participated extensively on any other SE site are likely the majority of these cases.
You should not do this repeatedly though, and it needs to be phrased as a suggestion rather than a command (e.g. "You might consider clicking the checkmark next to this answer if you want it to be marked as accepted"). If it's clear that the OP knows about accepting answers and is choosing, for whatever reason, not to accept an answer, then it will just come across as annoying or rude most of the time. Users are not forced to accept answers for any reason. Whether the OP accepts an answer or not is entirely their decision and there is no way we can force them to accept an answer (both morally and practically). It's also worth noting that accepted answers can be changed at any time, so there's no real reason to wait on accepting an answer except for psychological reasons since questions with accepted answers tend to not get more answers.
Luckily, it doesn't much matter whether individual questions have accepted answers. Questions with positive-rated answers count as answered (for the purpose of statistics) even if the OP doesn't accept any answer. And if the question has a good answer, future visitors will read it whether or not it's the accepted one. The questions on the unanswered tab don't just have no accepted answers; they also have no positive-scoring answers. Even a single answer with a score of 1 removes a question from that tab.
tl;dr: Only do this for new users when you suspect they aren't aware that the functionality exists, and you should phrase it as a suggestion. Don't do this to anyone who already knows about accepting answers. Also don't worry too much about this, since accepting answers really has almost no long-term effect.

88: <p>I just can't help to notice that there are quite a lot of questions that already have answers, and those answers are quite sensible but the user who asked those questions haven't accepted the answer yet. (You can reference to the <a href="https://anime.stackexchange.com/questions?sort=unanswered">Unanswered tab</a> for those questions)</p>

<p>Reasons might be because the user is still waiting for a better answer to come and I understand that. But when the question has been hanging for a quite a long time, the user who asked the question might already forget to accept the answer and the user who answered the question will be left hanging. Of course it will cause the user to be discouraged, since all of us would like to gain more reputations and badges. </p>

<p>I am referring especially to those new users who answered questions (and of course for all the users' benefit in general). For them not to be discourage and leave the site because they don't get any motivations (reputations or badges) when answering questions.</p>

<p>I suggest having the users check the questions they asked and validate whether there will still be a better answer to come (when the question has been not active for quite a time) and if they can consider accepting the answer available. This is my suggestion and it is okay for you guys to correct me if I'm wrong. </p>
 24: <p><a href="https://meta.stackexchange.com/q/88535/184716">This MSO post</a> is essentially asking about the same thing.</p>

<p>It is reasonable to suggest that the OP accept an answer if it's likely that they do not know about accepting answers. This is especially the case if they leave comments on an answer thanking the answerer. New users who have not participated extensively on any other SE site are likely the majority of these cases.</p>

<p>You should not do this repeatedly though, and it needs to be phrased as a suggestion rather than a command (e.g. "You might consider clicking the checkmark next to this answer if you want it to be marked as accepted"). If it's clear that the OP knows about accepting answers and is choosing, for whatever reason, not to accept an answer, then it will just come across as annoying or rude most of the time. Users are not forced to accept answers for any reason. Whether the OP accepts an answer or not is entirely their decision and there is no way we can force them to accept an answer (both morally and practically). It's also worth noting that accepted answers can be changed at any time, so there's no real reason to wait on accepting an answer except for psychological reasons since questions with accepted answers tend to not get more answers.</p>

<p>Luckily, it doesn't much matter whether individual questions have accepted answers. Questions with positive-rated answers count as answered (for the purpose of statistics) even if the OP doesn't accept any answer. And if the question has a good answer, future visitors will read it whether or not it's the accepted one. The questions on the <a href="https://anime.stackexchange.com/questions?sort=unanswered">unanswered tab</a> don't just have no accepted answers; they also have no positive-scoring answers. Even a single answer with a score of 1 removes a question from that tab.</p>

<p><strong>tl;dr</strong>: Only do this for new users when you suspect they aren't aware that the functionality exists, and you should phrase it as a suggestion. Don't do this to anyone who already knows about accepting answers. Also don't worry too much about this, since accepting answers really has almost no long-term effect.</p>
