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It is completely possible, although it usually involves social engineering (the real kind, not the bullshit in the section here).  You overestimate companies quite a bit too.  You'll also have better luck if you write your own exploits.

This post doesn't make any sense. You write exploits after already finding a vulnerability, I don't see how writing an exploit would better your luck or why you'd need luck after already finding a vulnerability.

The implication was that you also find the vulnerability, although even with existing vulnerabilities, it can be easier to notice if you use a common payload or exploit.

I genuinely have no idea what you just said. All I meant was that I don't know how writing your own exploit would make your success rate higher or why you'd need a higher success rate if you've already found an exploitable vulnerability.