This program is like a special diary writer that can write in two places at once! It writes a message in a book (a file) and also tells you the message out loud (prints it on the screen). It's like when you tell a secret to your friend and your mom at the same time!

Now, let's go through the thought process of writing this code:

1. We want to create a program that logs messages, but we want these messages to appear in two places: a file and on the screen.

2. First, we need to create or open a file to write our messages in.

3. We want to make sure we close the file when we're done, so we don't forget.

4. We decide to use a special writer that can write to multiple places at once.

5. We create a logger that uses this special writer.

6. Finally, we use the logger to write a message that includes a special number (the process ID).

Here's a breakdown of the code:

1. We set up flags for opening the file. These flags tell Go we want to:

   • Add to the end of the file if it exists (O_APPEND)
   • Create the file if it doesn't exist (O_CREATE)
   • Open the file for writing (O_WRONLY)

2. We try to open (or create) the file named "myLog.log" with these flags.

3. If there's an error opening the file, we print the error and exit the program.

4. We use defer to make sure we close the file when the program is done.

5. We create a MultiWriter that will write to both our file and to os.Stderr (which prints to the screen).

6. We create a new logger that uses this MultiWriter. We give it a prefix "myApp: " and tell it to include the standard flags (date and time).

7. Finally, we use the logger to print a message. This message includes the process ID (a unique number for this running program) which we get with os.Getpid().

This code demonstrates how to set up logging that outputs to multiple destinations simultaneously. It's a useful technique when you want to see log messages immediately (on the screen) but also keep a record of them (in a file). The thought process involves considering where we want our logs to go, how to set up the file, and how to create a logger that can write to multiple places at once.