Think of it like folks being born at a certain IQ, and you can really only maintain it (exercise, love, healthy eating, sleep, etc.) You can't bolster it beyond what is innate. However, you (and your environment, typically our parents) can definitely cause decreases in your IQ (poor sleep, anxiety, poor nutrition, toxins like lead, etc.)
I found it pretty interesting, but also kind of obvious in hindsight. I would love to be able to increase my IQ, as would many others, but we all gotta just work the best to maximize what we got. Maybe tech / gene manipulation will make it possible in the future though.
So, there are a ton of resources out there on how unreliable IQ is, and whether it's a valid indicator of general cognitive ability. Instead of linking them, I'll just link to the place that has the most good links:
https://en.wikipedia.org/wiki/Intelligence_quotient#Reliabil...
My understanding is that save for general statistical measures of a large aggregate, IQ is a poor measure for an individual (as it has been shown to change quite a bit for individuals over the course of a lifetime).
