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The strength of your opinion on Steemit is determined by the steem power you hold, whales have a lot of steem power. You should care because if a whale backs your content more people will see it, your contribution goes somewhere and is likely to get noticed and be valued by others. This is also how you get rewarded if you are trying to earn money.

You can spot one if it looks like this:

https://steemit.com/steemit/@deepsynergy/steem-whale-symbol

On the more serious note, the whale is someone who has accumulated a lot of STEEM POWER compared to other users in the blockchain. Often they are early adaptors of the Steem network.

A whale in a nutshell is someone with influence.
They have a lot of steam power and can make someone gain a lot in just one upvote and in turn cause a lot of other users to want to jump in and share in the quality of the whales upvote.

thanks for answering!!!

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