Laced up my shoes, holstered my water bottle, and set out to run five miles this morning, despite nagging doubts.
Despite nagging doubts, I just ran.
I ran without thinking: "Is this too fast? Should I slow down? If I don't slow down, I'll never finish," blah blah blah, etc. etc. etc.
Result? Ran my fastest four miles ever.
And then walked a bit and ran a bit for the last mile.
Total result? I ran five miles about one minute (ok, 1.6 minutes) faster than it took to finish my 8K (which, by the way, is 4.970969536 miles).
As a bonus, I discovered I was fine afterwards. I didn't die. The world didn't stop spinning. Nothing bad happened.
Stop thinking so much.