Never take things lightly. It can be very dangerous and many times people who take things lightly, suffer a lot. A simple example here is the Mumbai Test match(in late 2006) where our team took the English team lightly, due to the absence of major players like Trescothick, Vaughan, Harmisson (who missed out the last match). What the final result was that India were bowled out for 100 and England managed a series draw. That's because of not taking things seriously and absence of focus.
The reason for failures is lack of practice, taking things lightly without any proactiveness and absence of focus. India has many-many Arts, Commerce, Science and Engineering colleges in India - In fact Management institutes (Hotel, Business,etc.) are increasing day after day. But we notice a drop in Medical colleges as the focus required for MBBS is much longer. I am talking about a degree of 4.5 years, an Intership of 1-1.5 years, then practise study for 2-3 years and total Doctor would be studying for a period of around 10 years - the longest focus period required. A Doctor can never take things lightly. While Engineers play with Machines, Journalists play with words, Accountants play with numbers, Doctors play with Human lives. They have to have 100% focus in their task at all times. We don't need to be as proactive as doctors, but should be try and focus at least 50% of how much they do. There is no alternative to preparation in the real world for achieving success.
There are people who focus only on their goal and attain that without taking things lightly even for very small things. Bill Gates was a school drop out and he suffered a lot at that time, but he did not take things lightly. With extreme focus, he planned and executed his dreams and now he is the richest man in the world. That is not only because of work, but also because of his hard work. Gates used to sleep only for 4 hrs in the late 90s. Today, whatever product Microsoft develops, is automatically marketed. That is the power of focus.
Mistakes are bound occur as we all are human beings. But only few accept to mend the mistake. Failures are not the end of our part, it only takes some updates for your optimum success. Focus on your goals and with proper discipline and determination you can implement your dreams.