Leaving aside company founders who hit it big, the people I know who are the most successful (i.e., as employees), don't seem to be of above-average IQ, and man

Leaving aside company founders who hit it big, the people I know who are the most successful (i.e., as employees), don't seem to be of above-average IQ, and many of them have poor written communication (i.e., spelling, grammar, etc). What makes them successful is that they are good at interacting with other people, and they can communicate quickly and assertively and see to it that important things get done. Such people tend to work in customer-facing roles, such as sales, client-relations/customer-success, but they could also be in internal roles like marketing or management (including engineering management). But contrary to stereotype, the ones I've seen be effective are not insincere charmers/schmoozers, nor bullies. They are just fast-thinking and fast-acting and able to work their way through organisational barriers and ensure things get done in order to satisfy their customer or meet the business's requirements. On the other hand, I've observed that a lot of people who may be of above-average IQ are less comfortable with social interaction, and less able to engage in the kind of fast, confident communication you need to do well in an organisational context. It's not always the case of course - plenty of highly intelligent people are great communicators, and these people can do the best of all. But where a person of "high intelligence" does not achieve great success, low confidence/assertiveness/effectiveness at interpersonal interaction is likely to be a significant factor.