MCU serial port programming problem

I am working on dual-machine communication, but I have encountered a problem. The problem is this:
this works
while(TI==0);
TI=0；
……
……

This does not work. I cannot detect TI=1 using the following method. Why?
for(i=0;(i<10)&&(TI==0);i++);
TI=0；
if(i<10)
// Correct processing
else
// Error processing

There is no need to use the second method
It takes a certain amount of time for the serial port to send data. Assuming the baud rate is 9600bps, it takes more than 100 us per bit. If the data bit is 8 bits and the check bit is one, it takes more than one ms to send one byte of data. The error of the second method is that it is believed that sending does not take time or the time is very short. The author's original intention may be to make 10 judgments on TI. If TI is found to be 0 in all 10 judgments, that is, the sending is not completed, then it is considered that an error has occurred; otherwise, if TI is found to be 1 within 10 judgments, that is, the sending is completed, then it is considered that the sending is correct. The actual situation is that the time to execute 10 loops is much less than the time required for sending. Therefore, the loop has exited before the sending is completed, and a judgment of sending error is made. The correct handling is to add a delay program before the loop, and the delay time should be greater than the minimum time required for sending. I personally think that there is no need to use the second method. For the 51 single-chip microcomputer serial port, there are only the cases of sending completion and non-completion, and there is no concept of right and wrong. If the sending error is said, that is, after executing the sending instruction, the internal hardware circuit of 51 cannot correctly send the data or cannot set TI to 1, it means that the CPU is broken or the crystal oscillator has a problem. The so-called right and wrong should refer to whether the data received by the receiver is correct or wrong.