Sometimes we think we are failures, because what we do isn't as big as we had hoped it would be, or we don't have the worldly earmarks of success.
But more important than how successful we have been is how faithful we are. We may not know how successful we have been in this life, especially in our spiritual endeavors, until we get to Heaven. Those whom we thought were great successes may not have been as successful as we thought they were. And those whom we deemed failures may have been the greatest successes of all. We just don't know.
Before Jesus' disciples saw Him again after His death on the cross, they probably felt He had failed. I think the two disciples on the Emmaus road summed it up well when they were joined by the risen Lord, not knowing it was Him. They said, "We had thought he was the Messiah who had come to rescue Israel. That all happened three days ago" (Luke 24:21). These guys were so depressed that they left Jerusalem. They wanted to get as far away as possible from the scene of the crucifixion. Probably in their minds, Jesus had failed them. The others probably felt that way too. But when they saw the risen Lord, they found the opposite to be true. What seemed to be the end was really a new beginning.
Life can work that way too. Maybe something in your life right now seems like the end. But it might be a new beginning for you. God might be doing something above and beyond what you could ever imagine. So be faithful, learn from your mistakes, and keep moving forward.