Don't make these 2 big investing mistakes

This article said the big 2 mistakes are: 1) holding too much cash; 2) too diversify with too many transactions

http://money.cnn.com/2015/02/10/investing/big-investing-mistakes/index.html

I agree half la. 

1st of all, cash, yes, it will lose buying power as inflation will eat up the $$ in long run. But blindly invest in stock may kill you right away.

2nd, in theory, if you just hold an Apple or Disney (nothing else) for the past 10 years, you've made way much better than having say 20 stocks or an index fund (with 50-500 corporations). But there's two issues, 

1) it depends on what you hold (no one can tell whether Apple or Disney can continue to double for the next 10 years); 

2) depends on whether you have the patience to hold that long.

It is harder than many ppl thinks to hold that long.