If you're like me, your first easy runs were probably too fast.
Mine were. For a long time. I'd see "Easy 6 miles" on a Tuesday and run it at 8:30/mile, which felt right at the start — comfortable, conversational, the kind of pace you don't have to think about. By mile five my heart rate had climbed from 152 to 168 without me changing pace at all. I called it easy because it wasn't hard, and that's roughly when I had it wrong.
What "easy" actually means
Easy runs aren't defined by how they feel at the start. They're defined by how your body responds across the whole run. Heart-rate drift is a real thing. If your HR climbs ~15 bpm over a 45-minute run at the same pace, you were starting in zone 3, not zone 2. The pace I'd been calling easy was actually the bottom of moderate, and the difference matters.
I switched to running easy days closer to 9:30/mile, and 10:00 if it was hot or I'd lifted the day before. The first few felt absurd. Like I was barely running. But the HR stayed flat across the whole session, recovery the next day was noticeably better, and the hard sessions sharpened up within a couple of weeks.
Use heart rate, not pace
A pace target alone isn't enough. Easy pace depends on the day: heat, sleep, last night's lift, week 3 vs week 1 of a build. The same 9:30 that's easy in October is hard in late July.
The simplest rule I've landed on: cap easy runs at roughly 75% of max HR (or whatever your zone 2 boundary actually is; your watch's default for that may be off, mine was). If you cross it, slow down. Even if the pace feels uncomfortably slow. Especially then.
Why slow runs are worth the boredom
Easy runs aren't fun in the way intervals are fun. They feel like you're not working. You'll see other people's Strava feeds and want to push.
That's the tradeoff. Easy days do the thing speed days can't: they build the aerobic engine and let you actually absorb the hard work. If every run is moderate, you get pretty fit and then plateau there. (At least, that's what kept happening to me.)
Not the most satisfying lesson, but it's been the most useful one.