Phases in understand a paper

I have been reading the paer

Interface Decomposition for Service Compositions

I cannot understand certain approach in the paper, I keep reading it, but I still not able to understand it.

The main question in mind

 How it overcome the implied scenario?

(1)Email the author

The author refer me to a proof in the paper, this is the first breakthrough. But I can't understand the proof through.

(2)Use simple way(instead of the hard way) to understand it

I download the FSP, and find a implied scenario, and encode it in FSP, I gradually understand the approach in the paper.

The simple way here is: Hands on, and use the method on simple example. This almost apply in all scenarios.

The hard way here is understand it from the proof entirely.

(3)Defends it, know what exactly(a concise idea/argument) make it works.

But when discuss with a senior, who question about it's validity, I can't make an argument to defend it instantly. I keep handing on, and I more and more understand it, and make a very consice argument that why it works.