Mine was refusing to let go of the key sometimes. Figured it was time. Pretty easy to replace.

 

I saw a video on YouTube on how to check if the problem is your starter or all the circuitry involved with the ignition switch.

You remove the starter relay in the fuse box in the engine compartment.
Then use a jumper wire to short the contacts that put battery power directly to the starter.
If the starter works, the problem is not your starter.

In my case that is how I proved the starter was my problem,
I had issues where the starter would not even click or attempt to start, but the battery was good.
then when I wiggled the key around it would start.
So I replaced the ignition switch module on the left side of the steering column because a lot of posts say it goes bad.

Seemed to fix the problem, until one day it would not start in a parking lot.
I tried all the wiggling etc,
Then I tried the jumper trick to see if the starter would turn at all.
I did NOT. So I knew the starter was bad.

Since I was stuck in a grocery store parking lot all I could do was get an Uber and got get a starter and try to replace in it the parking lot.
But I gave it one last try and the F150 gods were helping me out and it started and I got her home.

I replaced the starter and all seems fine now..