The basic difference is if is a conditional, uncertain. Once is only pointing to a given moment of time, with no uncertainty whether the event happens or not.
They will attack at dawn. If we lose... No, not if. There's thirty of them against the three of us. Once we lose, don't surrender. You don't want to learn what they do to prisoners.
In your case, of the past sentences, once (b) makes much more sense: we already know it started snowing and the coaches canceled the game. You could transfer it into a conditional: we don't know what weather was at the game, so:
If it began snowing, the coaches would have decided to cancel the game.
In your question, the phrasing should make it clear, what the coaches will do:
If it begins snowing, the coaches will cancel the game.
If it begins snowing, the coaches will decide whether to cancel the game.
Now, the decision whether to use "if" or "once" depends whether you know it will be snowing or not. "Once" means you have a sure-fire weather forecast, you know that future event. "If" means an eventuality.
Win, Wins or Won? Which is correct?
- "Why condition1 and condition2 wins over condition3."
Example: "Why teamwork and ideas wins over smarts".
...etc.
Your clause -- "Why condition1 and condition2 wins over condition3." -- is typical for a title of an essay or article.
1. Which Aspect?
The given clause uses an aspect that indicates it's always true: in the past, present, and future. For that we use the present tense. This is called the "gnomic aspect", which uses the simple present in English to describe a general truth.
2. Is the subject singular or plural?
Next you need to consider the issue of whether the subject is singular or plural. The answer to this is based on whether or not you consider "teamwork and ideas" to be a single concept or two separable things. Unfortunately, this is not so easy with this subject!
2a. Maybe it's a singular subject.
A good argument can be made that you're pitting one thing (the combination of "teamwork and ideas") vs. another thing ("smarts"), and only one of them can "win". Thus we use the singular form of the verb:
- One thing wins over another thing.
- Why one thing wins over another thing.
- Why teamwork and ideas wins over smarts.
One could also say that if you use the singular form of the verb, you are in fact forcing the subject to be thought of as singular. In other words, plurality of the subject could be considered an issue of desired semantics instead of "correct grammatical style". However, this type of logic doesn't often win over fans of "proper" style.
2b. Maybe it's a plural subject.
Personally, I don't think so. But if you do think so, use "win".
Also, it looks very much like two (or more) separate things, so even if you consider them a single concept, it may "look weird" to use the singular. Some people will be unhappy with a singular verb form and will argue for the plural, "win".
3. "You can't win" (So change it.)
Unlike your proposition about "teamwork and ideas", you just won't be able to make everyone happy about either choice. But you can change it so it's more clearly singular or plural. The following is a singular subject:
- Why the combination of teamwork and ideas wins over smarts.
A good article on this can be found here: http://www.quickanddirtytips.com/education/grammar/compound-subjects.
Best Answer
The phrase you have provided is what's known as a negative polarity item (NPI) - a phrase that only appears in negative contexts - and uses the form:
2 is just a shortened version of 1, and tends to be more commonly used.
...so to use your example:
That being said, we tend to write "I could not help but laugh" - when speaking, the contracted form "I couldn't help but laugh" is more natural usage of the expression.