Let's talk about training tolerance and training stress.
Imagine your TOLERANCE for training as a bucket.
It gets bigger as your train more - within reason.
It gets smaller with all the OTHER stresses in your life - lack of sleep, poor nutrition, mental/emotional stress, etc.
Now imagine your training STRESS (what you do in a workout) as the water going into the bucket.
New exercises = more water. More weight/reps = more water.
The goal of a training program is to match the water to the size of the bucket.
If you get close to filling (or do in fact fill the bucket), your body will work to make your bucket bigger.
But if you overflow your bucket in a given workout, this is where soreness in the short term, dread for the workout in the mid-term, or even injury in the long term can happen.
So taking stock of how big your bucket is each day is important! Life stresses can make that bucket smaller - so listen to your body.