The TV anchor person announced, "Stocks have been rising and plunging dramatic this week." Pardon my disputing his word, but they didn't. They might have been rising and plunging dramatically--I've already lost too much to check it out. But they're not rising and falling dramatic.

How important is this tiny -ly ending? One illustration from a client document:
A permanent manned space station (means a permanent space station that's staffed)

A permanently manned space station (means a space station that is staffed 24/7--the station may or may not be permanent)

Adverbs tell more about verbs (and sometimes about adverbs and adjectives, and occasionally about the whole sentence).
Adjectives tell more about nouns and pronouns.

The manager speaks harshly. (Harshly is an adverb--tells more about the verb speaks.)
The manager's tone is harsh. (Harsh is an adjective--tells more about a noun, the manager's tone.)

The employee is productive. (Productive is an adjective--tells about the noun employee.)
The employee works productively. (Productively is an adverb--tells about the verb works)

The most common mix-ups happen when adjectives collide with verbs. That is, people mistakenly use the adjective form of a word (leave off the -ly) when they need an adverb.

Incorrect:

This product sells quick when the price is right.
He restructured the department careful so as not to upset people.
He invested his money cautious.

Correct:

The product sells quickly when the price is right. (how it sells)
Pongo restructured the department carefully so as not to upset people. (how he restructured)
He invested his money cautiously. (how he invested)

The manager is candid, but she speaks candidly. The proposal may be brilliant, but it's organized brilliantly. Pongo may have been careful, but he restructured carefully.

If the descriptor refers to the action (verb) rather than the person/place/thing/idea, add the -ly.