Because he keeps getting these big ideas and discovers he's in over his head and moves on to something else.
What Dibyayan really needs to do is pick some simpler projects, commensurate with his skill level and work towards the bigger goals. Balance the cheque book, do a houshold inventory, write a windows program, write a media player... along a progression of increasing complexity...
We see this all the time... people get through the basics, they learn the keywords, write the parking lot program and maybe the money changer, then decide they're ready for big time coding... Most often the result is that they frustrate themselves to the point of giving up on what could be a very rewarding career or hobby because they are constantly taking on projects they can't handle. I worked console projects for nearly 6 months before trying Windows GUI and worked that for nearly a year before letting any of it get beyond my own hard disk...
It needs to be said that what students learn --even at university level-- is usually just enough to qualify them to start learning... it's not a complete education and anyone who thinks it is, usually ends up repeatedly banging up against their limitations.
Even with the diploma in their hands, they still need to follow the learning process...