user16720: I have an ATtiny and am trying to send a very large byte array stored in a separate .h file over SoftwareSerial:
for (int i=0; i<numElements; i++) {
    softSerial.println(myList[i]);
}

I imagine it will very slow, which is fine, but I'm getting a cryptic error when compiling:
Firmware.ino.elf section `.data' will not fit in region `text'

It seems that this is due to the println() command running out of memory for some reason – if I comment out the println() command everything works fine. How to fix this?

user2881: The ATTiny only has a limited amount of RAM. A lot less that flash-memory.
Using a normal array, the entire contents of the array are placed into RAM (during initialization). Which is very limited.
I'd suggest, looking into PROGMEM. This is a way to read the data directly from the flash-memory. 

user37622: Your sketch doesn't fit into program memory of the ATtiny. If you comment out the println of the array, the compiler evaluates that the array is not used and doesn't attach it to the program. Then the program fits into memory.
EDIT
Chad suggests some good alternatives below, if you need to store more data than flash or PROGMEM will allow.

user41696: There is not enough room in program memory for 140KB. ATiny only has 8KB for the whole program. So there is no way to fix this with your current hardware. 
Options-  
add a storage device (SD card, sram module, others....) where you can store the data, and then read it in small chunks and send it out
possibly use a arduino mega. It has 256KB of program space. you will still have to make sure you are not trying to store the whole byte array in an array since that would get stored in sram (which there is still only 8KB) but it could again to written in chunks to avoid this problem. 

16720: <p>I have an ATtiny and am trying to send a very large byte array stored in a separate <code>.h</code> file over SoftwareSerial:</p>

<pre><code>for (int i=0; i&lt;numElements; i++) {
    softSerial.println(myList[i]);
}
</code></pre>

<p>I imagine it will very slow, which is fine, but I'm getting a cryptic error when compiling:</p>

<pre><code>Firmware.ino.elf section `.data' will not fit in region `text'
</code></pre>

<p>It seems that this is due to the <code>println()</code> command running out of memory for some reason – if I comment out the <code>println()</code> command everything works fine. How to fix this?</p>
 2881: <p>The ATTiny only has a limited amount of RAM. A lot less that flash-memory.</p>

<p>Using a normal array, the entire contents of the array are placed into RAM (during initialization). Which is very limited.</p>

<p>I'd suggest, looking into <a href="https://www.arduino.cc/reference/en/language/variables/utilities/progmem/" rel="nofollow noreferrer">PROGMEM</a>. This is a way to read the data directly from the flash-memory. </p>
 37622: <p>Your sketch doesn't fit into program memory of the ATtiny. If you comment out the <code>println</code> of the array, the compiler evaluates that the array is not used and doesn't attach it to the program. Then the program fits into memory.</p>

<p><strong>EDIT</strong><br>
Chad suggests some good alternatives below, if you need to store more data than flash or <code>PROGMEM</code> will allow.</p>
 41696: <p>There is not enough room in program memory for 140KB. ATiny only has 8KB for the whole program. So there is no way to fix this with your current hardware. </p>

<p>Options-  </p>

<p>add a storage device (SD card, sram module, others....) where you can store the data, and then read it in small chunks and send it out</p>

<p>possibly use a arduino mega. It has 256KB of program space. you will still have to make sure you are not trying to store the whole byte array in an array since that would get stored in sram (which there is still only 8KB) but it could again to written in chunks to avoid this problem. </p>
