Discount voucher

Few weeks ago, I received a 50% voucher posted to my mailing address from Ahava who is a beauty product brand like the face shop and skin food. With this 50% voucher, I"ve been thinking if I have anything to purchase from their shop and enjoy this so called 50% discount. However, I'm only using their hand cream and not intended to buy another 1 because I only used up like less than 20% after I purchased for more than half years.

So I went to that shop to check out if there is something suitable for me. After a glance, I saw their best selling shampoo and The price is not cheap. So I asked the sales girl if the voucher is applicable to everything in the shop. She said yes and then she lead me to one of their most expensive item and said "this is most worth it because you can save more". I took a look and realized the price is $84 and understand I would save $42 if I purchased that. It is a beauty serum that can help to replenish nutrient, refine skin and all sort of benefits.
I didn't buy it anyway because I forgot to bring the voucher with me so I told her I will come back again.

After that I went back and surfed from the net on the review of this beauty serum. Looks like the reviews are average good. With all the positive comment, I have decided to try it out, somehow I can save $42. Sounds great, right?
No, I didn't buy it at last and the voucher was expired 2 days ago. Reason behind is am I really need that beauty foru
? Am I really save of $42? From the beginning, i have nothing to buy from their shop. However, just because i want to fully utilize that voucher, I going to buy their highest range product to maxize my saving value. That is not right, right? I don't have to spend the 1st $42 to get myself a saving of $42! If I need this product, yes it has indeed a saving, but it's not for my case whereby I only want to use up the voucher and simply find somthing to buy.

I'm lucky finally I get this point and stop myself from spending unwisely.