For retail investors and "Gurus"; it is mostly likely to base on Hindsight Wisdom!
They pick a few stocks; all those stocks with TSR (Total Shareholder Return) of XX% over X or XX years become their evidence or proof that Value Investing or Deep Value Investing did work!
Those stocks that never make it; they are either mistakes or fairly valued.
Then they will move on to pick another few stocks. This value investing or deep value investing process will repeat all over again!
And then more evidence or proof that Value Investing or Deep Value Investing did work!