Selflessness comes not by discipline.
Selflessness comes by being aware of God's love for you.
When you think you have to earn God's favor (love, grace, approval) you are like a man who goes to work solely to earn money. He doesn't care about his employer. He only cares about his need for cash. Likewise when you think you have to earn God's favor you don't fully care about God, you are only trying to fulfill your need to be loved and approved of by God. Even the best intentions cannot get around this. Like the need for money we all have that need for God to favor us. The need isn't wrong but how we fulfill the need affects the way we live.
All of God's children already permanently have His favor through Christ Jesus. Only when you understand that you already have God's favor can you truly love God and live for others. With that understanding you aren't focused on fulfilling your need because your need is already fulfilled. You aren't living to earn but living to give out of the abundant loving-kindness that God has given you.
Being loved by our selfless God makes you selfless because you don't have to worry about your need. You don't need to reach to get, you simply receive. You trust that you are taken care of by God. There is no more loving way to live than to live loved.