Notice, accept, continue, enjoy
Notice
It is always painful to decide with which activity to stick. The same time keeping understanding the alternative costs of time. Alternative options, what I could be done. Taking coursera courses means I have to reduce time I spent on reading books. And each evening could be like this. Language learning versus twitter news. Writing versus reading. Taking rest versus sport. Movie versus documentary. Homework versus playing guitar. Party versus visiting old relatives.
Accept
Here it is perfect moment to stop and remember all good advices about being mindful in a moment. About accepting the thoughts, the doubts, the evaluation taking place inside the head constantly. Pay attention to them. Let them flow through.
Continue
Take your minds back. Concentrate of what you do, what you have decided to perform. Promise yourself time to reevaluate your choice later. But for current moment finish your task till some milestone. Start with smallest meaningful milestone. Simple as that.
Enjoy and have a calm evening.