Irrespective of the ages and professions, here we are having a concern on work, life and acquiring knowledge and experience balance.
The discipline you create for yourself helps you to maintain this balance and this balance is necessary because both are important, your work or studies you do, or the enjoyment and fun you want from life.
Time and task management plays a very important role here. Its true that 'all work and no play makes jack a dull boy, but all play and no work makes jack to get his future spoiled'.
Proper framing your schedule daily or weekly or yearly basis, helps you to make your work going smoothly with you having time to enjoy and experience the beauty of life simultaneously refreshing and enhancing your skills.
This actually helps you to experience the 'live in the moment' phrase, because you know what you have to do in that particular moment .The guilt of not getting to do things which we want to, have no place here.
And if something unplanned happens, we need to accept that, looking at the fact that we don't travel on same mistake again, as life is uncertain, we never know what miraculous we will get and then again adjust and return to our self-discipline and re-revise it as necessary.
That's how self-discipline is important to us so that we can be truly happy.