Both are grammatical and acceptable.
In short, the present perfect (have found) is more likely to be used when the speaker has no end time boundary in mind related to the context in which the past event (originally finding it) remains operative, carries consequences, or is of importance.
The present simple (find) is more likely to be used when the speaker believes--or for all essential purposes believes--that this finding (perhaps noticing instances of this truth) is eternal: a "permanent" fact about life or the world.
Very often, native English speakers would simply choose one or the other unconsciously, for a combination of reasons that we may be unable to understand or explain.
Whichever one you use, the essential meaning is likely "What Sinek said matches my own experience". It is probably of little or no importance, either to you (in your mind with respect to what you want to communicate), or to your listeners, when you began to find that this is true, how often you have found it to be true, etc. If it was, you probably would have added information to make that clear: ("I knew this to be true even before I heard it"; "I have always found this (to be) true in my own life"; "After reading this, I began to notice that it applies in my own life"; etc.)
Grammar texts tend to like to make black-and-white oversimplifications about things like verb tense usage. In reality, there are often numerous factors at work in determining many of our speech choices, each factor perhaps contributing in some partial fraction to a highly complex process complex.
The present perfect have found would tend to be used more often:
- In British English. There is a stronger expectation in BrE to use the
present perfect when the speaker does not wish to signal an ending
time boundary with respect to the consequences or relevance of a
finished past event or state. In American English, this is more often
a free choice. (Many grammars talk about this as "a finished past
event having a connection to the present," which I think is a pretty
useless description. Whatever you have just mentioned has a
connection to the present. You're talking about it!)
- If you have in mind, or want to suggest or emphasize that you
discovered this truth at some point in the past, or that it became
operational at some time in the past, as opposed to thinking or
wanting to communicate something more like "this has always been true
and always will be true". Though if this is very important or the
precise time that the event "found" occurred is relevant, the
statement would have likely been reformulated.
- When you have in mind or wish to communicate an idea that this is
something you have repeatedly noticed on distinct occasions (though,
again, if this is a definite or important part of what you're
thinking or want to communicate, you would probably re-phrase,
perhaps with "I have been finding ... ."
The present simple find would tend to be used more often when:
- You are "now" realizing or discovering this truth. "Now" here may
mean relatively recently.
- You believe this to be an "eternal", "permanent", or general truth
about people, life, the world, etc. It is boundless in terms of
Re: the BrE/AmE difference:
https://dictionary.cambridge.org/us/grammar/british-grammar/british-and-american-english (see section "verb tense forms").
More serious academic treatment : http://clu.uni.no/icame/ij33/ij33-45-64.pdf