You can never truly see yourself without some kind of tool, such as a camera or mirror. Usually, something else will be done to your appearance as well. A mirror flips the image horizontally. Other people, however, see you as you appear to the world. This does not only apply to how you look in a mirror, it applies to everything. Also, many people have differing views about things-- that is, everyone has their own opinion. Collectively, these opinions add up, and you probably want to go along or fit in with the highest opinion, similar to voting & elections. Seeking multiple opinions can help someone make a better choice because you cannot truly see yourself from an outside view, everyone has different opinions, and you may want to appeal to a group of people with certain opinions.

First, you can't see yourself. Again, this is meant literally, as said in the introduction, but also figuratively. You might think you know how people see you, but you most likely don't. Getting people's feedback on you is a great way to improve your personality and be a better person. In the end, nobody will really care about you if you just suck as a person and never get better.

The second reason for getting multiple opinions is that everyone has a different one. If you get the opinion of only one person, you have no idea if that opinion is the majority opinion or not. Sure, it is more likely for them to make up the majority, but they could end up being part of some group that makes up under 1% of opinions. If you want to get an accurate opinion on something you have to ask a lot of different types of people. The more people you poll/question, the more accurate of an answer you get.

Lastly, you may want to appeal to a certain group. For example, someone running for mayor will want to appeal to their city. If you want to see how you are doing, you can get someone to go around town and collect opinions on who they are voting for and why. Then, you can take those opinions and go from there, changing things if necessary. This will likely give you a significant boost by being able to take the general opinion of the public and appealing to them, landing you the spot in office.

Seeking multiple opinions is crucial to making a better choice because of the facts that you can't see yourself, everyone has a different opinion, and that you may want to appeal to a certain group. There are many more reasons than just these three. However, these were the three biggest reasons. Either way, there are still endless bonuses that come from it. Asking for opinions is absolutely free and perfectly normal, so why not do it for all the benefits it provides?