"When the sadhaka is firmly established in continence, knowledge, vigour, valour and energy flow to him"
We're talking the fourth Yama, Brahmachara. The loose definition of this sanskrit word is continence. But the words abstinence and celibacy often also comes about in when yogis talk about this.
Excess of any kind corrupts us; that's why it is called excess.
Perhaps the biggest challenge here isn't giving up things or actions. Building a daily life pattern that gives us enough of what we truly need without going overboard, or stopping to soon, is indeed a bigger challenge. This, of course, is the challenge of living our yoga practice.
For each of us, our definition of brahmacharya is going to be a bit different. The ideas of restraint and moderation shouldn't call for us to inflict pain upon ourselves. We'll be much better off in seeking alternatives to what we may be restraining ourselves from. This also means that every so often, we have to acknowledge, have and experience what we're restraining ourselves from in order to truly understand the value that is the absence of whatever we abstain from.
Many Christians give up something for Lent each year. When they rescind from their abstinence, many will have more appreciation and willingness to moderate their future indulgences. Muslims fast each year during Ramadan. Jews fast for various holidays. This idea isn't owned by any particular spiritual practitioner; all that is needed to make it valid is for the practitioner to be sincere in her or his devotion.
Other notes...
The "sadhaka" is the spiritual practitioner who has chosen a path of devotion. A "sadhana" is one's consistent yoga practice on and off the mat. Brahman is a high state of spiritual being that develops through practice.
