Ever done this?
Buy pattern while on vacation.
not the yarn recommended by pattern because that yarn only has yucky colors.
Make a point of not buying crochet hook for project, because you are sure you have that size at home and you've now decided to economize (after buying yarn and pattern).
Get back to the hotel and realize that you can't work on the knitting project you brought because your 4th double pointed needle was mysteriously left at home.
Curse yourself for not buying the $4 crochet hook.
Spend the rest of the evening listlessly flipping through the hotel cable channels.
Get home and realize, no you don't have that size hook after all.
Curse yourself further for not buying the $4 hook.
Decide that the yarn you bought is actually skinnier than the recommended yarn, so you decide to wing it with a smaller hook you have on hand.
Whip the hat up in an evening, and then impatiently wait for morning to come to see if the hat will fit smallest child, or if more cursing will be necessary before going to the store to buy the correct sized hook.
BUT huzzah! The hat fits! Smallest child LOVES it, and whooosh the hat soars out into the world to live a happy, colorful life...