Hindsight being what it is, I wish I had sold some

Hindsight being what it is, I wish I had sold some shares last run-up & doubled those shares on the dip. But, who knew? I believe that when it all comes together we will not see cheap shares, anywhere close to current levels again, ever. Therefore, I am AFRAID to try something like that for fear of having money on the sidelines when the sp takes off.