Like others have suggested, you don't necessarily have to upload everyday, but having a set video upload schedule may be a good idea. If you're able to create and upload a video everyday, then that's awesome, but many people simply don't have the time or may not have enough idea or content to produce daily videos. I don't think that's a huge issue, though, as long as viewers know when they should be able to expect new videos. This may still hold true once you have hundreds or even thousands of subscribers - there could be people who look forward to your content, so it's nice for them to know when they can expect new videos to be uploaded. Related to this, I also think that the type of content that one produces may have some impact on how frequently they can/should upload. I personally don't upload everyday, nor do I have a set upload schedule (which I should probably have), but most of my videos are tutorials, which may have a longer "shelf life" than, say, videos about current events or what not.