1. Do you think there is always an interesting photo to make?
Always, for sure. It only depends if I'm able and in the mood to see it.
It takes a certain relaxed awareness to see the little things that are constantly happening around me (particularly if I'm out to do street photography). If I'm too focused to shoot something very specific, then I will be prone to miss a lot of the unexpected situations that make street photography so exciting.
I try to shoot anything that catches my attention (gestures, little situations between people, odd folks etc.) without making any judgement, almost letting myself be guided by my subconscious mind. I find in this way that I am faster, missing less shots than if I thought a lot before deciding what to photograph.
Intention or the urge to bring home specific results or 'that super shot' are sure recipes for failure. If I have expectations, I often feel inhibited, kind of consciously weeding out all those occasions when I think there's something that might not work in terms of light, composition, or picture taking conventions. This makes me think too much, and then I tend to miss too many really interesting moments.
I often bring home a film / or a memory card full of what are 'boring shots' at first sight when I take pictures without great expectations. When I'm out with my wife, she often asks me 'did you take some good pictures today'? My answer is always unsettling for her: 'I don't know. Maybe I know when I had a look at them after I uploaded them to my computer / after I developed them'. This is because I consciously select pictures only in the editing process: That's when judgement of light, composition etc. makes sense, because then, I'm not risking to lose a shot, only to not discover a hidden gem (which will not go away then, but stay undiscovered in my archives).
So, there's always something out there to capture - the only question is whether I'm ready to see it.
2. More interestingly: do you play games or apply tricks to have a goal when practice shooting? After I got annoyed I decided to focus on shadows only and took 1 or 2 interesting shots with an interesting composition I think.
Absolutely, that's a worth-while pursuit sometimes, to hone one's capability to see photographically. I consider that as an analogy to a musician playing etudes - exercising my 'visual muscles'.
Of course, you could also use this in a different way - to pursue a project by shooting pictures for a certain look, topic or agenda. But that's quite a different photographic game ...