A proposal can be the surprise of a lifetime. Whether it's an intimate candle lit question, an extra-special holiday gift, or a grand family affair, a proposal can be a dream come true; or the beginning of a marital nightmare. If you can smell marriage in the air, or see the white dress and veil coming in the distance, the satisfaction of the tender experience may bring a smile to your face.

But when this magical moment seems to spring up out of nowhere, it may knock your socks off or knock you off balance. So before you make the arrangements, send the invitations or even hesitate at that all important "I do," here are 5 reasons why you should say "no" when he proposes.

1. The proposal is a way to prevent an exit

"Don't leave! Marry me, instead." If the surprise proposal comes directly after you've decided to call it quits, be suspicious of the promise of eternal commitment upon your return. There's no guarantee the marriage will even take place, let alone you two will have a harmonious union. Likewise, if the proposal is a seeming response to the threat of being left, make sure you put ample time between deciding to stay and saying yes.

2. It is merely a matter of convenience. 'I've settled on you.'

If there's been no real investment in the relationship so far, there's a good chance a proposal is making the statement "Let's keep things going," instead of "You're the only one for me." Before you think about setting a date, make sure neither of you is settling for less than you really deserve.

3. I need you... and your paycheck

If you're tempted to walk down the aisle because neither of you are sure if you can make it financially on your own, take a step back. Two incomes are certainly easier than one, but that's no reason to cheat yourself out of finding "the one." There are economic benefits to marriage, but it shouldn't lead the way to engagement.

4. A proposal can't fix a broken relationship

Belt out a big old "No!" if he pops the question once your relationship is already going downhill. An engagement will not save it; only hard work, an honest look at the problems, and perhaps professional help will save a dying relationship. A wedding will only make things worse.

5. 'I promise I'll change.' The proposal is a distraction from recent mistakes

If your mate makes a marital move after being caught or fessing up to being unfaithful or betraying you in another nasty way, keep engagement on the back burner until all of your issues have been worked out. If you decide to stay, definitely seek relationship counseling and make sure appropriate responsibility is taken for bad behavior. Don't let the glare of a diamond blind you to who you are about to marry. Put the question and jewelry back in the box and bring out all the secrets being kept in the closet.

When it comes to promises to commit, it's important to understand the motivation and intent of your mate. Find out not just why he or she wants to get married, but why he wants to marry - you. If your relationship has a history of issues, put in the time and work and create a new history first, then get engaged.