My biggest mistake, ever, was purchasing an overpriced investment property in 2007. 
For 5 years I buried my head in the sand and ignored the large negative equity that I had “invested” in.
I never missed a mortgage payment and maintained the property well.  The property was always rented.  However, the repayments were interest only, so they were not big.  I had paid €0 off the €200,000 purchase price.

In 2012 after listening to many interesting audio books such as “Think and Grow Rich” and “Getting Things Done” I decided to face my fear and figure out how I was going to manage this financial problem.  With the help of Microsoft Excel and approximately one hour of uninterrupted time, I realised that by working hard in my sales job, I could managed the debt and pay it off within the terms agreed.  I could even pay it off earlier, at a push.  I spent 5 years avoiding this one hour.

When in difficulty, by staying positive, listening to positive and successful people and planning a path to a better place can and does work.
There is no one that doesn’t get into difficult situations. 

For me, my biggest mistake has thought me so much about the importance of simple financial planning and working through difficult situations.  I hope it remains by biggest mistake, but as mistakes go, I thank it for teaching me a lot of very important real world lessons.

I am currently listening to “Total Recall” and am enjoying it very much.  Ordering “garbage” in the restaurant was very funny!