Your current best is evidence, not a lifetime contract.

What you have managed so far tells you something about what you had done up to that point. It does not tell you what you can do after another year of work, because the person who produced that result no longer exists in quite the same form. Treating your best as a fixed property rather than a snapshot quietly closes off the next stage.

When you catch yourself saying you are the kind of person who can only do so much, check when that measurement was taken. If it is more than a year old, it is probably out of date. Test it before planning around it.