Core business vs recreation

I always though that the core business should be the only thing to focus on in order to succeed. The 'core business' may be your work, university study or, last but not the least, your business. You have to give *all* the focus there is, invest *every* bit of your mind to achieve the prime aim - get that client, finish the project or hit the deadline. This theory always inhabited me subconsciously. But the essay by Paul Graham "The top idea in your mind" gave me the needed support. Thus, I started to think that there should be the only one top aim in my mind, hence, there will definitely be the top idea of which I will be thinking.
For example, if you want to finish your work backlog till the end of the month, do not engage in other activities like gym, learning Spanish or playing ball. Moreover, it is preferable to disengage yourself from the distracting activities at all. The less distracted you are, the more clear will be the success. Look alright.
But!
What if your chief aim is something really big that can take years to achieve - create million $ business, start a start-up or get PhD? Then you are going to be one on one with that chief aim till the success (or death :). No Spanish, no ball and, guess what, no gym. Even if it look alright to you, it may eventually get you down to disarming fatigue and failure.
What to do? Though patently simple it may seem, I suggest the following.
Write down what you want to be in, say, 3-5 years (PhD, 1M $ business, etc.) - the best situation if you have one chief aim or to fulfill, like get PhD. The clearer - the best. Now, you are going to invest all the mental energy and focus in this chief aim. You are going to manage your life in accord with the aim. As for other activities, let other manage it - find the teacher for Spanish, private trainer for the gym. Let other people in your life (no you) to manage and organize the recreational activities. All you need is to enroll and pay monthly. They will remind you and they will care.
In the end, you will have to care only about the chief aim - to manage, to plan and to succeed!