What is too expensive?

Why is it I will gladly spend $50 dollars on a nice dinner for the wife and I, but wonder if it is worth the extra $4 for the nicer insoles?  The food will be waste hours later but the insoles will be 6 months of happy feet. 

I'm sure many others do the same types thing. 

Like sleep on a bad mattress, but go on a cruise ever year. Would it make sense to skip the cruise this year and have a nice place to spend 1/3 of your day everyday for the next 8 to 10 years?

Why do we consider things for ourselves too expensive or not important?