There was an android project that I got from my senior.

he told me that another developer already completed most the project and all I have to do is minor changes...

Well when i saw, i was amazed that the code he commented is more than the actual working code without any structure.
He copied most of code from internet.

If it's not working, put in comment else use it.

It took me a whole month to figure out what's going on.

And another 2 months to fix the issues.

Well in last my senior told me that the developer took 1 year to write this code
(to be honest any normal developer can complete that project in less than 3 month)