<prompt> Human: Im 22 years old and expect my tax bracket to be much higher upon retirement. I have invested 5,500 into an IRA, with 3,000 in VTSMX and 2,000 in the MMA.I see the value fluctuating daily. Does it make sense to sell when its up, and reinvest the 3,000 to lock in the gains, and do this frequently? Say I see the value becomes 3,050. I can sell it, get 50, and then reinvest the 3,000 back into the VTSMX.Or am I supposed to keep the money in without taking it out and reinvesting?Edit: Thanks everyone, this definitely cleared things up! Ill leave it alone.  <response>: 3000 of VTSMX is not the same amount of shares as it was yesterday or tomorrow. Think of it this way.You have a loaf of bread 10 slices for easy math that you bought for 1000 its nice bread, okay?.After a month, you notice that the loaf is worth 1111. Sweet! So you sell the loaf of bread, put 111 in your pocket. Now youre ready to do this over again! However, when you go to buy another loaf, now they all cost 1111. For your 1000 you can only buy 9 slices. If you want a full loaf now you have to pay the 1111. Best to just keep the loaf you already had and watch the price go up.Why invest at all you say? If the price of everything just goes up?Well, if you had just kept the original 1000 in your pocket, today you could only afford 9 slices. 