They don't. They just gain expertise on subjects through trial-and-error and first-hand experience.
Anyone who tries to convince you that your should pay for advice on "how to become an expert" has expertise at only one thing: lying.
PS: I can teach you how to be an expert at spotting liars. For 5 dollars I'll tell you the secret.
Behind paywall 1: First lesson - don't pay for lessons on expertise. For 5 more dollars, I'll let you read chapter 2
Behind paywall 2: You are almost there! So close! You should be getting familiar with the trick by now. There was a secret lesson in part one. I'll tell the secret behind the trick for just 5 more dollars.
Behind paywall 3: Fool me once, shame on you. Fool me twice, shame on me. Fool me three times, and now we are here! Wanna know how I fooled you three times? Only 5 more dollars!
Now you are 15 dollars into spending 5 dollars on how to spot a liar. Just 5 more dollars!
Once you figure out the trick, you can consider yourself an expert.
Anyone who tries to convince you that your should pay for advice on "how to become an expert" has expertise at only one thing: lying.
PS: I can teach you how to be an expert at spotting liars. For 5 dollars I'll tell you the secret.
Behind paywall 1: First lesson - don't pay for lessons on expertise. For 5 more dollars, I'll let you read chapter 2
Behind paywall 2: You are almost there! So close! You should be getting familiar with the trick by now. There was a secret lesson in part one. I'll tell the secret behind the trick for just 5 more dollars.
Behind paywall 3: Fool me once, shame on you. Fool me twice, shame on me. Fool me three times, and now we are here! Wanna know how I fooled you three times? Only 5 more dollars!
Now you are 15 dollars into spending 5 dollars on how to spot a liar. Just 5 more dollars!
Once you figure out the trick, you can consider yourself an expert.