We all know this scenario ( or let me not generalize, but I know it). You have to get up for work during the week and every morning you feel like you will be able to sleep later, you cannot wait for the weekend, because then you are just going to sleep late and do nothing.....yes sure.
Come Saturday morning you are awake even earlier than in the week and you cannot fall asleep again.
I am sure there is a scientific explanation for this with the happy hormones your brain secretes, knowing it is weekend, or you inner voice that is more negative during the week, or whatever.
Another well known one is you are so tired at night, but is it only 8 o'clock - you know if you go to bed so early you will be awake half of the night, so you cannot wait for bed time, because you believe you are going to sleep like a log. Are you sure? Come bed time, a 1000 ideas and problems are running through your head at a 100 miles a minute, you cannot fall asleep and you know the next morning you will be a zombi, and so the vicious circle begins....
Nobody knows who this Murphy is or was who made this law, it is just a saying which originated in the 1940's and may have started with the armed forces of WWII, but we all know Murphy, has met him many time and we know he can be a real ass at times.
Other versions (or extras) of the law will be
and also
There are lots and lots of things getting blamed on poor Murphy.
This can all sounds very negative, but we cannot go through life always expecting the worst, always believing that thing are going well, so something bad will happen soon.
We know that life has its up and downs and everything that goes up, must come down, but what is down will go up again.
So just pack the bull (life) by the horns and run with it and if if throws you from one side to another, blame Murphy, dust yourself off, get up and shout