1) Boast not thyself of tomorrow; for thou knowest not what a day may bring forth.

2) Let another man praise thee, and not thy own mouth; a stranger, and not thine own lips.

You can't accomplish anything tomorrow, you can only do it today.  Planning for tomorrow is fine, but plans don't always work out, and the farther into the future you plan, the more likely it is that something will disrupt your plans if you haven't considered all possibilities.

If your the only one talking about your accomplishments, than maybe they were not as great as you thought.