Something Java and the Java ecosystem is terrible at. I've had project where we needed all of 7,8,9 and 10 [0] for the data stack: Hadoop, Scala, Spark, HDFS, zookeeper, pyspark. Good luck setting that up on a single machine, containers all the way. The java path nightmares I still have. I'm probably one of the few people in the word who know this much about the JVM without ever having written any Java.

[0] We should have also been following 11 but just didn't have the resources to even think about doing it.