Use what you know

Here is a good article on why you will always be more productive if you use what you know:

I spent two years trying to make Rails do something it wasn’t meant to do, then 
realized my old abandoned language (PHP, in my case) would do just fine if 
approached with my new Rails-gained wisdom.

Just after I launched QuickelSoft CMS 2, I had a contact with someone who wanted to launch a new version of his company web site and wanted to use QuickelSoft CMS to maintain its content.
He installed the Demo web site and created a lot of content items for his web site. He then “just” had to modify the ASPX templates coming with the Demo to match the look and feel of what he wanted. And at this point, he was blocked.

Why ? The existing web site was developed in PHP. 
I do not know very well PHP but compared with ASP.Net, the philosophy is different, the development tools are different.
So, he began to try to convert his PHP pages in ASP.Net. But it is not so easy if you do not know at all ASP.Net and have to learn it from scratch. So after some tests, he realized he would never have reached his deadline. And he chose to stick with PHP and started to look for another CMS.
He did not spent two years on his test but still, it was a waste of time for him.

It is something I should have anticipated during my discussion with him.
Even if the installation of the front end is not very difficult with no knowledge of ASP.Net, at the end, a template in QuickelSoft CMS is still an ASPX page.