The bad race you finished is worth more to your training than the good one you skipped.

A finished bad effort leaves you holding information: where it fell apart, what you could still do once it had, how you handle that particular feeling. A skipped good one leaves nothing but a story about how it might have gone. Training runs on real data, and real data is often unflattering. That is exactly what makes it worth having.

When you are tempted to skip something because it will not go well, do the ugly version and record what happened. One line is enough. Over a term those lines turn into the thing that actually tells you how to train.