What are effective methods to overcome the initial psychological resistance towards an unpleasant task? Background
Some self-help books note the difficulty of starting a boring or cognitively-difficult task (relative to maintaining the 'momentum' once the task has been started). Sometimes they describe an analogy to physical systems whereby a certain amount of 'activation energy' needs to be provided in order for a process to start.
Examples
To generate this initial energy, some self-help authors have described simple techniques:

The moment you feel an instinct or a desire to act on a goal or a
commitment, use the Rule. When you feel yourself hesitate before doing
something that you know you should do, count 5-4-3-2-1-GO and move
towards action.

Robbins, Mel. The 5 Second Rule: Transform Your Life, Work, and Confidence with Everyday Courage. Simon and Schuster, 2017.
See also: Is there any direct or indirect empirical support for the effectiveness of Mel Robbins&#39; five second rule?

Shrink your desired hyperfocus period until you no longer feel
resistance to the ritual. Minimize the amount of time you’ll dedicate
to focusing on one task until you no longer feel mental resistance to
it. Even setting a mental deadline of five minutes will likely be
enough to get you started.

Bailey, Chris. Hyperfocus: How to Work Less to Achieve More. Macmillan, 2018.
One could certainly enumerate an endless amount of techniques beyond these. For example, closing the eyes and visualizing oneself of performing the task, or one could pretend with a high degree of conviction that there is an infinitely large payoff for doing the task and an infinitely large penalty for not doing the task. However, it is not clear whether any of these methods would actually be effective.
Question
However, I have not found a single study that evaluated these, or similar, methods (i.e., interventions that increase the probability of people to initialize a psychologically unpleasant task).
What are effective methods to overcome the initial psychological resistance towards an unpleasant task?
Assumptions and differentiation from related questions
Kelly McGonigal distinguishes between I won't and I will willpower (see The Willpower Instinct: How Self-Control Works, Why It Matters, and What You Can Do to Get More of It (2012, ISBN 978-1583335086)). The former type of willpower (I won't) has been discussed in this Q&amp;A forum previously:
Best meditation techniques to overcome Behavioral Addictions?
Beyond CBT and MBI, what are effective behavioral interventions for modern lifestyle addictions during their engagement?
However, the question here is more in line with the I will willpower type.
I don't know of evaluations of those types of techniques. To broaden your query slightly, there is strong evidence from social psychology that increasing helpful behaviors and decreasing unhelpful behaviors is more about context than willpower (e.g., see how Nisbett &amp; Ross talk about the power of the situation for behavior: http://faculty.babson.edu/krollag/org_site/soc_psych/ross_pers_sit.html). So if a person were seeking to initiate difficult behaviors, I would first modify the context rather than use the tools mentioned. For example, if a person had trouble doing a work task and was using stackexchange as a distraction, they could disable their internet for a period.