A line can become confident because someone has erased many uncertain ones privately.

Confidence in finished work is nearly always the residue of private failure. One clean stroke exists because dozens of others were tried and removed where nobody could see, and what looks like natural certainty is accumulated correction. This is why comparing your rough attempt with somebody’s final version is so discouraging and so misleading. You are seeing their last try beside your first.

Give yourself somewhere to be uncertain that nobody else reads: a rough page, a draft, a version you promise to throw away. Do the deciding there. The confident version is the one that comes afterwards.