I think there are reasons, and there are excuses.
A Reason is something you cannot control.
An Excuse is something you can control.
Can't squat because you have a broken knee? That's a reason.
Can't squat because you are sore? That's an excuse.
Can't train because your project at work went haywire and you have to stay until after midnight and then be back in the morning? Reason.
Can't train because you had a hard day at work and feel tired? Excuse.
It can be hard to tell the difference sometimes. The test is simple, though - can you do something about it? Will you?
Will you deal with your muscle soreness and go train anyway?
Will you make up for that missed workout the next available time?
Once you've established something is a reason, you can often nibble away at the edges. For example, I do poorly with sprints. I have exercise-induced asthma, so if I push to my physical maximum running or sled pushing or rowing or whatever, I can stop breathing properly and require medication. It can wreck me for days as I recover. But what I can do - and have done - is push back the margin of how much work I can do before triggering an attack. I've learned where that edge is, and push right up to it. I've expanded my range even if I still have to keep a safety margin.
So asthma is a reason, not an excuse. If I just said, well, I can't go hard on my cardio . . . that would be an excuse.
Accept that which is truly limiting you, but question those limitations. Is there a way around it? If you can't control that, find the next closest related thing you can control and take charge of that.