There is a lot of psychology that goes into the whole universe of gambling, and anybody who has ever logged onto their online casino or stepped into a physical casino environment could probably tell you all about it. There are mathematics that govern all of these games, but invariably emotions can take over for some people. And one of those emotions is pure fear.
What is that fear of? Well, many things. One of them is the fear of failure. You simply don't want to not emerge victorious, because the feeling of inadequacy comes along with it. And then there is also a fear of embarrassment. When you look at a poker game, for instance, you might, on any given occasion, observe people at a table with those who are much more experienced than they are. And there are fears on the part to the novice that the more experienced guy is going to make them look bad. It's something the player will feel within himself as much as it is the appearance that he will give off in front of the other players. No one wants to look bad, obviously.
Some of this probably explains what makes players so tentative in certain situations. In blackjack, for example, there are folks who will not hit a 12 or anything higher, no matter what, simply because they are afraid to bust out, and therefore want to stay in the action for as long as possible.
Blackjack is a game that is played against the house. They don't necessarily do anything proactively to exploit a player's fear. Poker, on the other hand, is a different animal entirely. A veteran player can sense the fear and weakness of another player, and they are usually going to be happy to exploit that for all it's worth. They will be quick to challenge a vulnerable opponent, and this is particularly troublesome in no-limit hold'em games, where a player could be eliminated quickly. And the player who fears this may happen may tend to adjust his or her approach in order to avoid that potential pain. And then the thing just starts to snowball.
Or, it could come back to work to your advantage. That is, if you have made such adjustments in such that you are taking measure to minimize your fears, or work around them somehow. Of course, if you are on the other side of the equation, and sense that somebody you have encountered is encumbered by fear, you had better be in a position to seize the moment.