I'd say the same is true for entrepreneurs. It usually takes at least 2-3 years for a young and fresh entrepreneur to hit his own stride and know what works for him the best.
In listening to both of them, I heard something that I have found to be true in my own experience. It takes time to learn how to be an early stage investor. You have to make a bunch of investments and learn from them. And you have to develop a strategy, a thesis, and your own differentiated style which people can then attach to you. In effect you have to build a brand and become known for what you do and how you do it.
None of this happens overnight. I think it took my friend about four years to hit his stride. I suspect it took the Gotham Gal about as long. Part of this is that is how long it takes to know if you've made a good investment or not. You might know in two to three years. But by four years, it is going to be pretty clear. As these outcomes start coming in, you can start to see what is working and what is not.
And "what is working and what is not" is not just about your investment selection. It is about the fit between you and a certain kind of entrepreneur and a certain kind of target market and a certain kind of business model. Some investors are better at investing in SAAS companies. Some are better at investing in e-commerce. Some are better at investing in mobile apps. Some investors are better at working with teams that need a lot of help. Some investors are better at working with teams that don't need any help and want you to get out of the way.
It is important to figure out who you are and where you fit in the startup economy before you can become a good investor. But once you do that, you can "hit your stride" and start investing with conviction.