Setting personal goals
Imo, setting personal goals requires a balance between holding yourself accountable and not self-blame for missing an overly ambitious target.
One of the most common type of personal goal is "New Year Resolutions". Every year, some people will set (and even publicly announce) what they plan to achieve for the upcoming year. Many however, falls short on actually completing them and repeats this cycle next year.
As @DThompsonDev puts it, don't wait for the new year to change. Change can start anytime of the year whenever you decide to start. Start now instead of waiting for the right time!
It's probably hard to "punish" yourself for missing a target so instead, you could try positive reinforcements. One common mistake is to reward yourself before you even started. This gives you little incentive to actually achieve the goal.
Instead of buying a new pair of shoes to motivate yourself to pick up running, commit to actually run 5 days a week for 2 months before rewarding yourself with that new pair of shoes. (Unless if you don't have a decent shoe to run in at all, get something cheaper for now.)
On the other end of the spectrum, some people would self-guilt heavily for not hitting a specific (and often overly ambitious) target. While it's important to self reflect on what one could've done better, it's also important to not spiral into self-blaming.
Focus on setting better goals, better milestones, better way to track progress, and even tweak the goal (and timeline) if needed. This process is different from person to person.
Personally, I usually set relatively vague goals and only focus on 1 or 2 things at a time so it's easy for me to always reset / recalibrate and be like, am I still on track or did I got distracted and side-tracked away from my goal? Maybe I should reset my goal?
Side tracking isn't always bad. It's only bad if you constantly side track and never finish any one thing. This takes long term effort to track if it's a larger pattern. Otoh, it's also important to reevaluate and set new goals if you've decided to move towards a new direction.