The below short story can inspire you to grab the opportunity at first instance as it knocks once and one has to be ready to identify and catch the same, failing which one can be standing aside a fence and keep regretting in life.
A young man wished to marry the farmer's beautiful daughter. He went to the farmer to ask his permission. The farmer looked at him and said, "Son, go stand out in that field. I'm going to release three bulls, one at a time. If you can catch the tail of any one of the three bulls, you can marry my daughter."
The young man stood in the field awaiting the first bull. The barn door opened and out came the biggest, meanest looking bull he had ever seen.. He decided that one of the next bulls had to be a better choice than this one, so he ran over to the side and let the bull pass through.
The barn door opened again. Unbelievable. He had never seen anything so big and fierce in his life. It stood pawing the ground, it eyed him. Whatever the next bull was like, it had to be a better choice than this one he thought. He ran to the fence and let the bull pass through.
The door opened a third time. A smile came across his face. This was the weakest bull he had ever seen. This one was his bull, he said to himself. As the bull came running by, he positioned himself just right and jumped at just the exact moment. He threw his hands to grab..... But alas..... The bull had no tail.
Moral of the whole story is that one has to understand this fact that the Life is full of opportunities and one has grab the same at the first instance. This same analogy also applies to the stock market traders where they have to identify the opportunity at first instance and have to lock on with it at first instance to make money in the market.