Is it true that the simple past tense is connected to the present, but the present perfect is not? Is it true that the simple past tense and the present perfect tense are identical in their time relationship to the present?
Past Simple: I lost my keys.
Present Perfect: I have lost my keys.
The first sentence tells us only about past event, but we do not know what happened later. The speaker may have found the keys later, so although he lost the keys he has it now.
The Present Perfect sentence shows the connection with the present, so if someone says I have lost my keys, he means that he does not have it now.
The time relationship to the present is also different for those 2 tenses.
A sentence in Past Simple can tell about events in any time. It can be either very close past:
I saw an interresting film on TV yesterday.
or very distant:
Columbus discovered America in 1492.
Present Perfect is used to speak about events close to present:
You can say I am not hungry, I have just eaten lunch which tells about a close past.
It is not correct to use this tense to talk about events in the distant past. You cannot for example say:
Chineese have invented printing
Although this event has (great) influence on present world, it is too distant in time to use Present Perfect.