A LOW TIME GRUMMAN PLT TAXIED ONTO; AND DEPARTED FROM; HOU'S RWY 12R WITHOUT CLRNC.

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I WAS DEPARTING THE ARPT (HOU) AFTER ROUTINE MAINT AT THE LCL FBO. GND HAD CLRED ME TO RWY 12R VIA TXWY K. UPON REACHING TXWY K AND RWY 12R; GND CONTACTED ME AGAIN TO ASK IF I WAS READY TO GO. I ACKNOWLEDGED; AND I HEARD GND REPLY 'OKAY; RWY 12R; MONITOR THE TWR ON 118.7.' ALTHOUGH I THOUGHT IT ODD; I THOUGHT I HAD BEEN CLRED. I REPLIED 'CLRED FOR RWY 12R; MONITOR TWR;' AND BEGAN ROLLING IMMEDIATELY. JUST BEFORE SWITCHING TO TWR FREQ; AND UNFORTUNATELY ALREADY ALIGNED AND ROLLING AT FULL PWR; I HEARD GND CALL ME. ON TWR FREQ I HEARD TWR ORDER ANOTHER ACFT TO HOLD ON BECAUSE HE HAD A GRUMMAN TAKING OFF THAT HE WAS NOT TALKING TO. THAT DOUBT I HAD ABOUT GND GIVING A CLRNC WAS CONFIRMED. I IMMEDIATELY CONTACTED TWR AND EXPLAINED MY ERROR AND WAS GIVEN VECTORS AND INSTRUCTIONS TO CALL THE TWR WHEN I ARRIVED AT MY DEST FIELD. FORTUNATELY; I MADE MY MISTAKE DURING A VERY QUIET POINT ON WHAT IS NORMALLY AN EXTREMELY BUSY ARPT AND DID NOT CONFLICT WITH ANY ARRIVING OR DEPARTING TFC. I THINK THE GREATEST FACTOR IN THIS INCIDENT WAS MY HURRY TO GET OUT OF THE WAY FOR WHAT IS A NORMALLY VERY BUSY ARPT. CONTRIBUTING FACTORS WERE NOT HEARING EXACTLY WHAT I EXPECTED; GENERAL FATIGUE FROM WORK STRESS; AND A DESIRE TO GET HOME. I HAD EXPECTED GND TO GIVE ME EITHER A 'HOLD SHORT OF' OR 'POS AND HOLD' INSTRUCTION. INSTEAD OF CLARIFYING MY INSTRUCTIONS BEFORE PROCEEDING; AS I HAVE DONE IN THE PAST ON SMALLER ARPTS; I CHARGED AHEAD FOR FEAR OF TYING UP ARPT TFC. PREVENTION OF PROBS LIKE THIS REST WITH THE PLT. IF YOU'RE IN DOUBT; STOP AND CLARIFY. DON'T LET THE PRESSURE OF THE ENVIRONMENT RUSH OR OVERWHELM YOUR DECISION MAKING PROCESS. IF YOU'RE IN THE WAY AT A BUSY ARPT; LET CTL TELL YOU YOU'RE IN THE WAY; AND THEN LET THEM TELL YOU EXACTLY WHERE THEY WANT YOU TO BE. IT WOULD BE HELPFUL IF ALL TAXI INSTRUCTIONS TO A RWY CONCLUDED WITH EITHER 'HOLD SHORT' OR 'POS AND HOLD' TYPE INSTRUCTIONS. IF YOUR INSTRUCTIONS ARE SOMETHING YOU FEEL YOU NEED TO PUZZLE OUT OR INTERPRET; OR IF YOU THINK TO YOURSELF; 'WHAT EXACTLY DID THEY MEAN BY THAT;' THEN ASK 'COULD YOU CLARIFY WHAT YOU MEANT BY THAT?' DON'T LET WHAT YOU EXPECT TO HEAR CONVINCE YOU TO TRY AND INTERPRET WHAT YOU DID HEAR. BETTER TO BE GRIPED AT ON THE GND FOR HOLDING UP GND TFC THAN TO RISK A POSSIBLY FATAL TANGLE WITH AIRBORNE TFC.