Any practice requires some discipline.  In yoga, the word 'tapas' means discipline and also means 'fire.'  The fire of discipline helps us stay present to all the wavering modifications of the mind.  Discipline also requires balance.  We must learn when to rest and when to let go. Here's an inspiring video of what sustained discipline can cultivate:

[youtube]8SbXgQqbOoU[/youtube]

(Thanks, Elizabeth)