By definition, you will spend most of your time not at your best.
This is true on all dimensions: how you feel, how fast you run, how likeable you are, how much you like other people, how well your body works, how well you write.
It’s also true of everyone else – so you’re going to need a lot of grace and forgiveness, or this is going to get ugly.
How much are you likely to need? I suggest going with your gut, then adding half as much again, and then another 10%.
Then double it and keep it in your pocket for the mistakes and not-at-our-bestnesses that you’re likely to encounter just around the corner.