Have you ever reached a barrier in your training? Can't break 5 minutes in the mile, 11 seconds in the 100 meter or a 405 pull deadlift. You've been training for that specific thing for some time now and your not getting any closer to reaching your goal. Welcome to the Law of Accommodation. Learn it well if you wish to progress. Simply stated the law states that after a certain amount of time your body will no longer accommodate to the same stimulus. You will learn to run at the 5 minute mile pace. You're body can't get any stronger from the work you've been doing day in and day out to get you over the 405lb deadlift.
Your body needs change, but before you go and get crazy, it still needs specificity. How can you have both? You need to change it up to elicit a new response, but elicit a response that will help in your ultimate goal. Will starting out a 5k training program help your deadlift? Absolutely not, but increasing your glute ham strength will. Maybe you do a specialized sled dragging program for 6 weeks, got in and retest the deadlift. You will be quite surprised.
Run 800 repeats at a 4:50 mile pace. Gradually bring the rest intervals down. Your introducing a new speed for your body to adapt to. Maybe you do a 3 week core/hip strengthening program. Now your left glute med isn't allowing your pelvis to collapse and your cruise to a 4:55 mile.
The body is an amazing organism. It will adapt to what you throw at it. But only for so long. Keep throwing new things at it, that will challenge it for the greater goal. That's the Law of Accommodation.