Not only will it make the character bland, but it'll make the plot bland as well. There has to be a reason for the main character to be fighting the external forces. If something just randomly attacks him and he fights and beats it easily, then there isn't a plot.

Next, there can't be external conflict without internal. They might be afraid of what they're fighting, they might not want to do something, they may have several choices to weigh that all seem equally favorable at the moment. There is always internal conflict, however small, and a good writer will tap into this and show it to the audience. Not only does it make the audience understand the writing better, but it will also show the character and their personality, and it will make the reader feel what the hero is feeling.

If somebody reads that somebody is attacked by a bear, they'll wonder if they should care. Showing the emotions and conflicts the character is facing will make the reader imagine themselves in the hero's place, and the story will gain excitement and meaning.

Also, don't forget to show the villain's conflict as well. The villain isn't just a punching bag for the hero, they're also people with feelings and reasons for being villainous. They weren't born bad, some internal conflict drove them in that direction.