Here is another one from the same Quora post as the next answer.
Let's say you were cooking a pasta primavera and the following tasks needed to be completed:
1) boil water (takes ~5 mins)
2) throw pasta in water
3) wait for pasta to cook (takes ~10 mins)
4) cut vegetables
5) pan fry vegetables (takes ~5 mins)
6) heat sauce (takes ~5 mins)
7) mix it all together
Notice there are certain tasks which take a longer amount of time, but you aren't just going to put water in a pot and watch it boil. In the meantime, you might decide to work on #4 and if you finish that fire up another stove and start #5.
There's only one of you, just like there's only one process in node.js... yet you can still multitask by starting "blocking" operations (in our cases anything involving heating) and moving onto other things while you wait for them to complete.
Node works the same way. There's one process with a single thread, but you can write code in such a way that things that take a long time (disk I/O, network I/O, etc) can be interleaved with other operations.