Keep trying! It so often happens that the last key opens the door. Likewise, it is your last prayer that may grant you salvation, and your last meditation that may grant you realisation.
Successful meditation entirely depends on our inner cry. When a child is hungry, really hungry, he cries. He may be on the first floor and his mother may be on the third floor, but when the mother hears his cry she comes down immediately to feed the child.
Let us take meditation as an inner hunger. If we are really hungry, our Father Supreme will come running no matter where we are crying. If we have intensity and sincerity in our cry, then we begin to make spiritual progress immediately. Otherwise, it can take years and years.
Again, God-realisation is not like instant coffee-something that you will get immediately. God-realisation takes time. If somebody says he will be able to make you realise God overnight, then do not take him seriously. It takes twenty years to get a Master's degree, which is based on outer knowledge. God-realisation, which is infinitely more important and more significant, naturally will take many more years. In no way do I want to discourage anyone. If your inner hunger is sincere, then God will satisfy that hunger.
If we practise concentration and meditation regularly, we are bound to succeed. If we are really sincere, we will reach the goal. But the difficulty is that we may be sincere for one day or for one week, and then we feel that meditation is not meant for us. We want to realise God overnight. We think, "Let me pray for one week, one month, one year." After one year, if we don't realise God, we give up. We feel that the spiritual life is not meant for us.
The road to God-realisation is long. Sometimes, while walking along the road you will see beautiful trees with foliage, flowers and fruits. Sometimes you will see that there is only a road, without any beautiful scenery. Sometimes you may feel that you are on an endless road through a barren desert, and that the goal is impossibly far away. But you cannot give up walking just because the distance seems far, or because you are tired and have no inspiration. You have to be a divine soldier and march on bravely and untiringly. Each day you will travel another mile, and by taking one step at a time eventually you will reach your goal. At that time you will definitely feel that it was worth the struggle.
Love the battlefield of life, for joy is always breathing secretly and openly in both your victory and your defeat.