On top of our performance gains coming from ticking off the core fundamentals with running (and doing them consistently enough) there is a lot to be said about experimenting with your training to find a balance/approach that works for you.
For example, during intervals you may find one pace works out a bit too quick on certain reps, or hampers your recovery, so you adapt, scale back and go slower. You may find your body runs best on certain days of the week, after a day off running or the day after running.
Essentially, don't be afraid to make mistakes with running. If something dosen't work in a session, in a long run or anything, instead of viewing that as a personal failure, use that knowledge to adapt your training and make you a stronger, wiser, and better runner going forward.
This from my experience is most conspicuous with weekly mileage. There's nothing wrong with experimenting with what works best for you mileage wise- It is a personal thing after all. As long as you abide to the running fundamentals and adapt mileage build up progressively and gradually (particularly for those new to the sport), and as long as you can consistently do the sessions to a good quality and recover well you are on the right track.
With this said, a lot of the time we can identify our weekly mileage threshold by experimenting with it. This should really be a one off thing, but once you know your limits with weekly mileage, you can then work within your threshold and make sure to get the right training built in. Again, like before, this will probably result in you feeling overworked and finding it difficult to train, but by making this 'mistake'' you have identified your limits and know how to train smarter and more effectively going forward.
The trick is to do what works best for you and what responds well. Don't get hung up on what other people do. Cameron Harris- Head Coach