As Goldilocks would say about porridge goals need to be “just right”: not too easy and not too hard relative to your skill level. I use the SMART model for crafting goals and the A and the R ensure that they are not too hard. To ensure they are not too easy I always look to set stretch goals. If my target is X I will specify X+1 in the goal. It is achievable if I put the effort in, perform well and circumstances allow. If I do not achieve X+1 then I learn for next time.
Neurologically a goal where the challenge is low and skill is high generates a low arousal spike that may manifest consciously as boredom.
Optimal performance is where the goal is moderately hard in that it has high challenge and requires high skill as it will generate a bigger, but not too big, arousal spike that lasts longer.
A goal we perceive as impossible in that the challenge is high and beyond our skill generates an over aroused “fight/flight” spike which may manifest as anxiety and possibly a physical fight or flight response.
When you specify goals use the SMART model and ensure they are just right in terms of ambition: not easy, not impossible, a nice challenge.