There is a simple Rule of moving averages which says, buy above if price closes above it, and sell if prices closes below it...it is well known by every TA aspirant...And in 'n' number of books you must have read this...that if you invest according to this you will loose your money...
But here i am having a different opinion(based on my own testing)...Rule works if you know what position sizing you are adopting it in different times...
A simple example is, if stock 'x' is below 200 and 50 sma...but recently it coming above 20 sma..this is still a buy case for me. it its coming out of long base building, and yes my capital allocation cant be full...as price is still below 200 and 50 sma...
In another example, let us assume stock is severely above 50 and 200 sma...almost a parabolic run up. so in this case you cant go on with full allocation defined in your rules...As you know stock is well overextended...
Moral for me, is defined your rules...and most important thing i learned is money management...position sizing...There are different times one needs to be learned, you just cant go full throttle...sometimes you need to slow down for taking a little turn ahead...