The end of the year is just an arbitrary marker on the time continuum. 

However, our brains respond well to such arbitrary markers - new year, birthdays, anniversaries, etc. These markers provide ways to divide the time continuum that we experience. Rather than all of it being one big muddle where we recollect a lot more of what has happened in the recent time and forget a lot more of what has happened in the not so recent time, these markers help establish some groupings of time that we can recollect separately and remove the effect of recency bias, at least to a certain extent.

And while looking forward, we tend to be a lot more optimistic about what we can get done in the immediate future and a lot more pessimistic about what we can get done in the distant future. There has evolutionarily been not much incentive to plan months and years ahead while there has been reinforcing pay-offs for planning just a little bit ahead.

Due to this, we tend to overestimate what we can do in the immediate future (short term) while we tend to underestimate what we can do in the distant future (long term).

This is where arbitrary markers that are yearly in nature come in handy. 

While we might underestimate what we can get done in a year, taking the deliberate action of setting ourselves yearly goals will help us correct for the under-estimate and push us to be more ambitious and realistic at the same time. 

We can re-evaluate how we've been faring, set ourselves new goals or simply course-correct on our path to goals we are already pursuing on any random day. And it works just as well.

However, it is a little bit easier on one of the arbitrary markers because our brains are primed for such an exercise as they are already perceiving a transition. 

Moreover, this is also a time when a lot of others undertake a similar exercise, thus allowing us to conform, which is another reason why arbitrary markers work well on our brains.

Only question is, will you make use of it?