To put a twist on this thread, have you ever refused a run with someone slower than you because they train too fast, or been refused by a slower runner because you train too slow?
I'm not fast, but I run 10k maybe 3-4 minutes quicker than the buddy in question. I run my easy days easy, and my hard days hard. He runs every day hard - well, not really hard, per se; he runs every run at about 6:30 to 7:00, never goes much slower, but never does anything much faster/harder (except hill repeats).
I used to call him up to run (and vice versa), but we've drifted apart because when we do run together, I'll set out at maybe 7:30 pace (+/-), and he wants to run 6:30. I don't mind going slower on easy days, but I don't like going much faster, and I draw the line at going any quicker than, say, 7:00 pace.
It was kinda comical a few times, we'd be out for a run chatting, and next thing you know he's 100 yards ahead of me, then standing around waiting for me to catch up, hoping I'll move up to his pace.
Anyway, lotsa different circumstances can make two runners incompatible as training partners.