To answer seriously, take a rest day every week. Take a rest week (lower voulme, but still some intensity) every 4 weeks.
Go f'n hard on interval days. And completely ignore average speed.
You're problem was you never went easy, and there could never go as hard as you could either.
Go really hard when the schedule calls for hard and really easy when the schedule calls for easy.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.